Sweet dreams are made of cheese
Neuroscientists have successfully sent sleeping mice into REM sleep by activating a small group of neurons in the medulla with an optogenetic stimulus, according to a paper published in Nature.
Now entering dreamland
Researchers from the University of California, Berkeley, used optogenetics to insert a switch into specific neurons in the medulla, an ancient part of the brain, that enabled them to activate or inactivate neurons with laser light.
Activation of this group of nerve cells caused sleeping mice to quickly enter REM sleep. REM sleep is the dream state in mammals accompanied by activation of the cortex and paralysis of the skeletal muscles. Inactivation led to a reduced or eliminated ability to enter REM sleep.
Yang Dan, Professor of Molecular and Cell Biology at UC Berkeley, said: “People used to think that this region of the medulla was only involved in the paralysis of skeletal muscles during REM sleep.
“What we showed is that these neurons triggered all aspects of REM sleep, including muscle paralysis and the typical cortical activation that makes the brain look more awake than in non-REM sleep.”
The researchers, whose work is published in Nature, hope the discovery will allow scientists to develop a better understanding of how sleep and dreaming are controlled within the brain and help us to learn why we dream.
UC Berkeley postdoctoral fellow and first author Franz Weber said: “Many psychiatric disorders, especially mood disorders, are correlated with changes in REM sleep, and some widely used drugs affect REM sleep, so it seems to be a sensitive indicator of mental and emotional health.
“We are hoping that studying the sleep circuit might lead us to new insights into these disorders as well as neurological diseases that affect sleep, like Parkinson’s and Alzheimer’s diseases.”
Hungry or sleepy?
Further investigation into the function of these nerve cells showed that activation, while the mice were awake, did not make them fall asleep, but it encouraged them to eat more. In normal mice, these cells (a subset of neurons that release GABA neurotransmitters) are most active when the mice are eating or grooming, pleasurable activities.
The team thinks these GABAergic neurons in the medulla have the opposite effect to stress neurons, such as noradrenergic neurons.
Professor Dan said: “Other people have found that noradrenergic neurons, which are active when you are running, shut down when eating or grooming. So it seems like when you are relaxed and enjoying yourself, the noradrenergic neurons switch off, and these GABAergic neurons in the medulla turn on.”
Professor Dan is continuing her studies of the neurons that affect REM and non-REM sleep.
Paper reference
Weber F, Chung S, Beier KT, Xu M, Luo L, Dan Y Control of REM sleep by ventral medulla GABAergic neurons Nature 526: 435-438 (2015) doi: 10.1038/nature14979
Sign up to receive our latest news
Find out about Scientifica's latest product releases, company news, and developments through a range of news articles, customer interviews and product demonstration videos.
)